Hello I will help you with your question,
Yes this means the computer cannot access part of its internal memory like a PC whose hard drive has bad sectors so the PCM/ECM needs to be replaced.
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Yes the PCM and ECM are different names for the same part. Sorry you will need to replace the computer.
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will this affect engine performance? Should i replace rite away or can it be driven for awhile?
Eventually the vehicle will no longer start, it might be the next ignition or it might be several months but eventually it will fail completely. Replace as soon as you can
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The new computer will learn the security from the body control computer but the VIN and mileage will have to be entered into the new computer either at the dealer where the computer comes from or by the installing technician at the time of installation.
Let me know what questions you have